 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
174.18.26.131
In Reply to: RE: Which versions? posted by 1973shovel on November 10, 2023 at 03:32:49
That's probably why I've kept the original 12AT7 board all this years. If I were to buy a new VTA amp, the 6SN7 board would be a no brainer. I've also heard the newer versions of the ST70/ST120 now feature dual rectifier tubes. Let's just say I'm tempted.
Follow Ups:
When I bought my blank board, the VTA 12AU7 circuit had recently been released. There was a lot of praise for it, and since I didn't need the AT7s added gain, I populated the board to use 12AU7s, not knowing any better.
One of the things on my 'must try' list of cures was going to be to convert the board to use 12AT7s. I was told by those in the know here that the AT7 would be an improvement over the AU7 from a linearity standpoint, but not by a lot.
The single voltage gain 6SN7 solved that decision for me, since it's more linear than either the AT or the AU. I sometimes wonder if 6SN7s in the phase inverter positions would further improve things. But given this is just a back-up amp for me, I'm happy enough just having it be something that I no longer dislike.
I liked the original VTA ST70 (12AT) from the start. After a few weeks of run in, it proved itself clearly superior to my previous CJ MV75A1. That said, I'm tempted on a couple fronts. I have the 6SN7 adapter on hand if I want to give that a shot, but I'm even more tempted to do the entire board. The other temptation (at roughly 10X the cost) would be the newer version of the ST70 that features dual rectifier tubes along with the 6SN7 option. Right now the 6SN7 board is a much better for for my budget. And FWIW, my friend who has the VTA ST120 has had all 3 boards and clearly prefers the 6SN7 board.
With but a few resistor changes to the voltage amplifier (center) tube, you could easily convert that to use a 6SN7 via your adapter. for a couple of bucks and a little bit of soldering, it should give you a good idea of the changes the full 6SN7 board might bring.
I'm thinking of converting my phase inverter tubes from 12AU7 to your 12AT7, since I already have some NOS JAN 12AT7s in stock.
I appreciate your feedback on your friend's preference for the 6SN7 board. As I noted elsewhere in this thread, Roy Mottram said 90% of his customers preferred the 6SN7 board over the 12AU7 version. It's hard to argue with 90%
"I'm thinking of converting my phase inverter tubes from 12AU7 to your 12AT7, since I already have some NOS JAN 12AT7s in stock."
I will be very surprised if this produces any audible or measurable improvement regarding distortion. The LTP is inherently "linearized" due to internal feedback, just like a cathode follower. My last amp used a 6J6 LTP and managed < .035% THD at 5W output. Curves for the 6J6 clearly don't support this level of performance.
That's one less thing to 'obsess' over!
Thx. Although I could easily live with the 12AT7 board, I will most likely proceed with the entire 6SN7 board. My tech is only 2 miles away and he has that board on hand. He used to be Bob Latino's builder for the amps shipped west of the Mississippi. And the board swap is reversible if for some reason the 6SN7 experiment didn't pan out. I'll let you know how it all shakes in the next month or so.
...and since you already have the adapter, changing out only six resistors to use one 6SN7 (which is also reversible) would save you money. That's why I suggested it.
And despite what I just read on the VTA forum by someone there who should know better, a 6SN7 is decidedly not just an octal 12AU7. The noval version of the 6SN7 is the 6CG7, not the 12AU7. The 6CG7 (and the octal 6SN7) is a far more linear tube than the 12AU7 on paper (see link below), and in many people's opinions, including mine, it sounds far better.
Note that a 6CG7 is NOT a direct plug in replacement for a 12AU7, as their pin-out is different, which is accomplished in the 6SN7 adapter.
Good luck with it, and I look forward to hearing your take on the 6SN7 board.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
